The debris produced includes particulate matter and dust. To reduce the dispersion of dust into the environment, which has deleterious effects on both equipment and personnel, the debris is sprayed with water. The water is supplied with the air through the drill string to the drill bit and in addition to suppressing dust also causes corrosion, in particular of the bearings. It also produces a slurry which causes wear of the cutting surfaces of the drill bit, reducing the life of the bit and reducing drill penetration rates. The drill bit is a costly item to replace.
A stabiliser may be located behind the drill bit to centre the drill bit within the borehole. The sections of the drill string are joined together by threaded connectors at either end. Two standard threads are generally used in the drilling industry, namely BECO and API, and a crossover connection is often required to accommodate assemblies having these different threads.